Apparatus for the sputtering of materials



June 23, 1970 F. GAYDOU ET AL 3,516,919

APPARATUS FOR THE SPUTTERING OF MATERIALS Filed Dec. 16, 1966 United States Patent 3,516,919 APPARATUS FOR THE SPUTTERING OF MATERIALS Francois Gaydou, Balzers, and Rudolf Jenne, Triesenberg, Liechtenstein, assignors to The Bendix Corporation, Rochester, N.Y., a corporation of Delaware Filed Dec. 16, 1966, Ser. No. 602,398 Claims priority, application Switzerland, Dec. 18, 1965, 17,502/65 Int. Cl. C23c 15/00 US. Cl. 204298 1 Claim ABSTRACT OF THE DISCLOSURE The present invention relates to an apparatus for the sputtering of materials by means of a low voltage electrical discharge. The improvement consists of providing a hot cathode separate and spaced from the material to be sputtered and closely surrounding the material to be sputtered by an anode. This physical arrangement, aided by a magnetic field, provides an improved sputtering rate and permits the sputtering process to proceed under lower pressures.

A material disadvantage is experienced with the sputtering of materials by introducing them into an electrical discharge in that the rate of sputtering is relatively small so that, for example, the production of thin films, according to the known cathode sputtering process, is especially tedious. Efiorts to eliminate this disadvantage have not been lacking, in particular, one has attempted to intensify the sputtering through increasing the ion energy, that is to say, through the use of higher accelerating potentials.

Another definite disadvantage of the known sputtering technique exists in that, almost without exception, it must be carried out in a relatively-high pressure gas atmos phere in order that sufiicient ions may be available. An improvement has been achieved through the use of magnetic fields which act to lengthen the path of the charge carriers in the discharge so that sputtering can be done at lower pressures.

The present invention has as it goal a new apparatus for electrical sputtering which brings with it a significant increase in the sputtering rate, requires no great expenditure and aifords a safe operation with relatively-low voltages and lower pressures than have been permitted heretofore.

The apparatus according to the invention for the sputtering of materials by means of a low voltage electrical discharge between a hot cathode and an anode is characterized in that the surface of the material to be sputtered is surrounded by the anode.

A preferred form of carrying out the invention will be considered in which the anode surrounding the material to be sputtered is formed in a ring or square shape.

The invention will be explained in detail with the aid of an example of its execution. In the accompanying drawing 1 designates the bell jar or vacuum housing of a vacuum equipment for the production of thin films into which a work holder 2 is introduced onto which substrates are fastened, for example, glass plates 3. For this purpose, the material to be sputtered, in the form of a plate 6, is arranged in the equipment on an electricallyconducting support 5 carried in through the baseplate by an insulator which, in the sense of the patent claim, is surrounded by the anode 7 formed in a ring-shape. The latter is supported by the metal cylinder 8 (with the opening 9 for the escape of air during evacuation) and connected by the conductor 10 and the voltage lead-through 11 with the positive pole of a direct current source of voltage. An electron-emitting hot cathode 13 is provided 3 ,5 16,919 Patented June 23, 1970 in a separate chamber 12, flanged to the bell jar 1 for the production of the gas discharge, resulting in sputtering. In operation, the discharge takes place between the cathode 13 and the anode 7. The valve 14 is available for the introduction of gases in which the discharge takes place. The gas in question, for example Argon, is introduced through the conduit 15. The necessary heating current for the hot cathode, located at ground potential, is received through the current leads 16. In order that the gas admitted through the valve 14 can be better ionized by means of the hot cathode 13, an aperture 17 is provided, which throttles the outflow of the gas and thereby permits a higher gas density in the chamber 12 than in the vacuum space 18 below this aperture. It is worthy of note that the intensity of the discharge is hardly, noticeably limited in the described apparatus in spite of this aperture and the further limitation of the discharge cross section by the relatively small Opening 19 in the work holder 2 and in spite of a lack of a direct line of sight between the cathode 13 and the anode 6. In the operation of this apparatus, discharge currents of 30 amperes at anode potentials of, for example, 60 volts were immediately achieved, during which the gas pressure in space 18 must be maintained at not more than 10- to 10- torr. Of course, at the same time, a magnetic field of a few hundred Gauss was utilized parallel to the axis 20 of the equipment which was produced through the magnet winding 21 surrounding the bell jar 1 and a negative auxiliary potential of 1,000 volts was applied to the plate 6 of the material to be sputtered (as is shown in the drawing).

With the described apparatus, one is permitted to achieve, in a surprising way, very much higher sputtering rates than appear to be possible with the classical cathode sputtering apparatus in which the material to be sputtered itself forms the cathode and no supplementary hot cathode is provided.

It is further to be noted that it is expedient that the gas admitted by the valve 14 is continuously pumped out of the equipment through the opening 22 by the vacuum pump connected to it at such a rate that exactly the desired gas pressure is maintained in the equipment. This method of operation has the advantage over the use of a stationary atmosphere that the pressure adjustment is independent of the variations due to the uncontrollable gas absorption on the walls (getter eitect of the sputtered material).

An alternating potential source, preferably high frequency, can also be connected in place of the mentioned negative auxiliary potential, especially for the sputtering of dielectrics.

As is well known, an additional auxiliary electrode can be provided in the neighborhood of the hot cathode in order to facilitate the ignition of the gaseous discharge. A positive potential of a few hundred volts is applied to it through a current limiting resistance for the ignition.

We claim:

1. A sputtering apparatus for depositing thin films of material on a substrate, which comprises:

(a) an enclosure having an upper chamber and a lower chamber, said chambers communicating with each other;

(b) means for evacuating said enclosure, said means communicating with said lower chamber;

(0) means for providing an ionizable gas to said enclosure, said means communicating with said upper chamber so that gas admitted to said upper chamber is continuously pumped out of said enclosure through said lower chamber :by said evacuating means at a predetermined rate to maintain a pressure in the lower chamber of at least 10 torr;

(d) means for sustaining a discharge in said enclosure,

said means including an anode having a cavity located in said lower chamber, and a thermionic cathode located in said upper chamber;

(e) a plate of said material to be sputtered located in said anode cavity, so that the periphery of the surface of material to be sputtered is surrounded by said anode, said plate being separate and independent from said anode and cathode;

(f) means for mounting said substrate in said lower chamber so that the surface of said substrate faces the surface of said plate;

(g) means for applying a positive potential to said anode; and

(h) means for applying a negative potential to said plate to attract ions and cause sputtering of said material from said plate onto said substrate.

References Cited UNITED STATES PATENTS ROBERT K. MIHALEK, Primary Examiner SIDNEY S. KANTER, Assistant Examiner 

